Obstructive sleep apnea (OSA) affects up to 15% of the population with a prevalence higher in men than in women and increases with age, with obesity as the most recognised risk factor. OSA manifests as disrupted breathing during sleep, causing a general decrease in life quality of patients, including daytime sleepiness and reduced cognitive function. OSA has been shown to be influenced by both environmental and genetic factors, where the later has resulted in several studies focusing on possible associations between different genetic variations and prevalence of the disorder. Some studies have found association with a single nucleotide polymorphism at the promoter region of IL-6 (IL-6 -174G/C), which has been suggested to alter expression of the inflammatory cytokine interleukin-6. In this study 261 Swedish OSA and 70 non-OSA patients, all having coronary artery disease (CAD), were genotyped at IL-6 -174G/C by polymerase chain reaction - restriction fragment polymorphism, and statistical analyses were conducted to assess suggested potential association between the disorder and allele frequency at this position. Earlier reports regarding this has shown conflicting results and we found no significant association between IL-6 -174G/C and prevalence of OSA, nor with selected clinical parameters. However, a significant association was found between the IL-6 -174C allele and occurrence of daytime sleepiness in abdominally obese Swedish OSA patients with CAD. Our results confirm and extends some earlier findings indicating an intricate relationship between multiple clinical, genetic and environmental factors and the complexity of OSA, pointing to the need of further studies.